Preparation of hot-pressed coal briquette with the extract from direct coal liquefaction residue

Direct coal liquefaction residue (DCLR) is an industrial by-product from the direct coal liquefaction process. It is harmful to the environment and the human body when directly charged or used due to the high content of sulfur, ash, and polycyclic aromatic hydrocarbons (PAHs). Therefore, it is of great importance to treat and utilize DCLR. In this paper, the thermal extraction method was applied to extract DCLR with N-methylpyrrolidone (NMP), and the hot-pressed coal briquette (HPCB) was prepared with DCLR extract and anthracite powder. DCLR and its extract and residue were characterized by TG, FTIR, and GC-MS. The ash content was decreased from 11.72% to 0.72% and the sulfur content was decreased from 1.72% to 0.09% after thermal extraction. TG analysis shows that the weight loss of the extract was about 30.4% higher than that of the residue during the pyrolysis process, indicating that the extract contained more light components. FTIR analysis shows that the thermal extraction process had strong extraction capacity for aliphatic hydrocarbons and aromatic hydrocarbons, but weak extraction capacity for carboxyl, phenol, or alcohol groups. GCMS shows that 60.6% of the volatile substances in the extract were PAHs, while the residue had only 6.8% of PAHS. It is proven that the residue has been rendered harmless to humans and the environment. Moreover, the HPCB with a compressive strength exceeding 2.5 MPa was prepared by using the DCLR extract as a binder and anthracite powder as a raw material. It has the potential and advantages of being used as a metallurgical raw material.